Create your first Spring Boot Web Application
Create your first Spring Boot Web Application

In last tutorial we have learned about the Advantages of Spring Boot and Spring Boot Installation. Now we should create a small application to learn how to create your first spring boot web application from scratch.

This tutorial explains how to Create your first Spring Boot Web Application using STS (Spring Tool Suite).

STS is an Eclipse-based development environment that is wonderfully customized for developing Spring based applications.

Lets learn how to create spring boot application.

Creating Application using STS

Following are the steps to Create your first Spring Boot Web Application

  • If you don’t have STS already installed, download and install the latest version of STS from the following link for your respective Operating System:https://spring.io/tools
  • You should see the following screen upon opening STS for the first time.
  • Select the workspace directory path to store your project code as below or keep the default path suggested by STS:
STS Workspace Directory Selection

  • Click on the Launch button after selecting the workspace directory.
  • Right click on the Package Explorer.Select New -> Spring Starter Project to create a spring boot project in the following screen:
Spring Starter Project Selection Screen
  • After selecting the Spring Starter Project, as shown above, you can choose the options (like Packaging Type, Java Version, package name, build tool, Name of the application, etc) for configuring the Spring boot application using the following screen and click on Next.
  • On clicking Next as shown above, you can select the Spring Starter Project dependencies.
  • First, Select the Spring boot version. In this case, it is 2.1.3.
  • Since we are trying to create a web application, we need to select the ‘Web’ dependency from the List as shown below and Click on Finish:
Project dependencies screen
  • Once done, examine the project hierarchy and notice that all the dependent Maven dependencies automatically to the classpath and this is the main power of Spring boot.

Note: In the below screen, all the Maven dependencies gets downloaded automatically.

Maven dependencies screen

It was the responsibility of the developer to carefully select the compatible versions of the dependent libraries to make the application up and running before the introduction of Spring Boot.

However, with the introduction of Spring boot, it downloads all the required libraries automatically, just by mentioning the Spring boot version and Web dependency as shown in above “Project dependencies screen”.

Project POM.xml

  • Examine the auto-created project’s pom.xml and notice the following main tags:
Project POM.xml
  • spring-boot-starter-parent: This parent declaration downloads all the Basic Spring libraries into the CLASSPATH.
  • spring-boot-starter-web: This dependency downloads all the web application libraries required. Also, it provides the following advantages:
    • For instance, note that tomcat embedded server dependencies get downloaded as well.
    • Thus, we do not need to install and configure Tomcat separately for deploying Spring boot application.
  • spring-boot-starter-test: This dependency imports both Spring Boot test modules as well as:
    • JUnit

Main Class

  • Examine the following source code in DemoApplication.java under src/main/java package which is the starting point for the Spring boot application.
  • For instance, in the following code, the main() method uses SpringApplication.run() method to launch the application. 
package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

  public static void main(String[] args) {
    SpringApplication.run(DemoApplication.class, args);
  }

}

Please note in the above code, @SpringBootApplication annotation is present.

@SpringBootApplication single annotation is equivalent to including the following 3 annotations:

  1. @Configuration: Indicates that the class is a source for bean definitions.
  2. @EnableAutoConfiguration: It sets and configures beans based on the CLASSPATH entries. Auto-configuration classes get applied based on the CLASSPATH and the beans which are defined.
  3. @ComponentScan: Spring can auto-scan all the classes with this annotation and registers it with the Application context when the Spring application starts.

Web Application Controller Class

  • Now that we have a main class, let’s now create a web application controller that handles incoming web requests.
  • For example, refer HelloWebController.java present under same package like in below example DemoApplication.java :
package com.example.demo;

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;

@RestController
public class HelloWebController {

@RequestMapping("/")
public String index() {
return "Hello World!!";
}
}

Above annotations @RestController and @RequestMapping are described below.

  • @RestController – This annotation indicates that this class handles Web MVC requests.
  • @RequestMapping – This annotation is defined on the method to invoke based on the incoming request path.

In the above example, all requests coming with ‘/’ are mapped to index() method and returns a plain text message: “Hello World!!

Running the Application

  • Till now we have learnt how to create your first Spring Boot Web Application. Now its time to execute it.
  • You can run the application created just like a java application by : Right click on Main Class -> Run As -> Java Application.
Running the Spring Application

Console Output

  • Open the Console window to see the following output:
Console Output

Testing the Application

  • You should see the following output rendered by the browser:

Conclusion

In this tutorial, you have learned about how to create your first Spring Boot Web Application and how to run your first Hello World spring boot web application. Next tutorial will explain about the Spring boot Build Systems and Starter module.

References

https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#getting-started-first-application

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